The purpose of this research is to investigate more fully with, quantitative procedures, certain preliminary experiments which suggest that the thymus derived cells involved in the initiation of the humoral immune response are similar to, or are the same thymus derived cells involved in the initial recognition aspect of cell mediated immunity reactions such as the delayed-type hypersensitive foot pad swelling reaction of sensitized mice. This will be accomplished with the aid of an in vitro short term culture technique which allows the measurement of T-cell cell cooperation activity, and activity measured by the enhancement of an in vitro primary anti-hapten immune response. Limiting dilution techniques will allow the establishment of a minimum number of units responsible for such immune responses. By manipulation of the antigenic stimulation of mice, it will be possible to establish some parameters of the "lymphocyte traffic" of functional immune cells in the mouse and will allow some understanding of the critical parameters involved in the balance between the initiation of the humoral immune response and the expression of cell mediated immunities against certain antigens. Bibliographic references: Kettman, J. and Lesley, J. The in vitro induction of specific unresponsiveness against the 2, 4, 6-trinitrophenyl determinant. II. Prevention and reversal of the unresponsive state. Cell. Immunol., 17, 1-10 (1975). Kettman, J. and Dutton, R.W. Role of antigen in the immune response. Analysis by limiting dilution methods. Cell. Immunol., 17, 228-239 (1975).